Large distillation columns used for air separation are typically constructed in fabrication shops and then transported to their installation sites via roads and waterways.
The main distillation column typically includes a two-column system for nitrogen-oxygen separation featuring a high-pressure column and a low-pressure column, which are arranged one on top of the other, thereby forming a “double column.” A main condenser, which is generally disposed between the two columns, is constructed as a condenser-vaporizer and allows for heat-exchanging communication for the high-pressure column and the low-pressure column. The distillation column system, in addition to the nitrogen-oxygen separation columns, may additionally include further apparatus for obtaining high-purity products and/or other air components, in particular noble gases, for example an argon production apparatus comprising a crude argon column and optionally a pure argon column and/or a krypton-xenon production apparatus.
A “cold box” as used herein is to be understood as meaning an insulating enclosure, which completely encompasses a thermally insulated interior in outer walls; plant components to be insulated, for example one or more separation columns and/or heat exchangers, are arranged in the interior. The insulating effect may be brought about through appropriate engineering of the outer walls and/or by filling the interspace between the plant components and the outer walls with insulating material. The latter version preferably employs a powdered material such as, for example, perlite. Not only are the columns and the main heat exchanger enclosed within the cold box, but other cold plant components are enclosed by one or more cold boxes as well, which can make the resulting cold boxes quite large.
The external dimensions of the cold box usually determine the in-transit dimensions of the package in the case of prefabricated plants. The “height” of a cold box is to be understood as meaning the dimension in the vertical direction based on the orientation of the cold box in plant operation; the “cross section” is the area perpendicular thereto (the horizontal). The longitudinal axis of the cold box and column is the axis parallel with the height. In transit, the cold box is shipped in a horizontal fashion, and therefore, the height of the cold box determines the in-transit length and the cross section determines the in-transit height and width.
Air separation packages are typically fabricated in a factory, which is generally remote from the installation site of the air separation plant. This allows some substantial prefabrication and hence some minimization of the construction requirements at the installation site, where conditions are often times more unpredictable. The prefabricated package or packages are transported from the factory to the installation site, the cold-box package with one or more separation columns in a horizontal arrangement. Package length and width are subject to restrictions for this kind of transportation. This technology has hitherto only been used for medium-sized air separation plants when the columns are at least partly packed with structured packings, since packed columns generally require a greater installed height than plate columns.
In installations using relatively large columns, a lower degree of prefabrication is typically used due to the unavoidable transportation constraints, and therefore, more actions must be undertaken on-site. This is particularly true for the cold box, which for larger plants, is typically erected and installed at the installation site once the columns and other equipment are already in place.
Therefore, there is clearly a need for a manufacturing method and device that would allow for larger air separation plants to be delivered and installed with a minimal amount of installation time by using prefabricated packages.